sub process_log {
    my ($log, $pattern) = @_;
    my @index = grep {$log->[$_] =~ m/^$FAILURE_SEARCH /} 0 .. $#$log;
    print "INFO: $log->[$_]This occurred on line $_\n"
        foreach @index;
    return join '', map {$log->[$_]} @index;
}

my $problems = process_log(\@Log, $FAILURE_SEARCH);